1. Field of the Invention
The present invention relates to a composite film having a gas barrier property. In particular, it relates to a gas barrier film suitable for use in the packaging field requiring a high gas barrier property or use as a substrate for various kinds of displays, or use for covering a substrate.
Moreover, the present invention relates to a gas barrier film for a display substrate or suitable for the display covering application, to hardly generate expansion or distortion derived from heat or moisture at the time of processing or use, and a substrate film therefor.
Furthermore, the present invention relates to a display using such a gas barrier film.
2. Description of the Related Art
Nowadays, various types of displays are used or discussed for their practical uses. Except the cathode ray tube type, all of them aim at a thinner configuration. Furthermore, those of the flexible type are being requested. Then, use of a synthetic resin sheet or a synthetic resin film is being discussed instead of the glass substrate conventionally comprising the display. Furthermore, in order to prolong the life of the display, covering the display with a gas barrier film for blocking a color developing element or a light emitting element from the external oxygen or water vapor has been discussed. The terms “sheet” and “synthetic resin film” refer to those having a relatively thin thickness of about 100 μm or less, however, in the present invention, the film and the synthetic resin film refer to both those having a thick thickness and those having a thin thickness.
Conventionally, in the field of packaging such as food packaging, various kinds of gas barrier films with the gas and the moisture content permeating property restrained (that is, the gas barrier property provided) by forming a thin layer of a metal oxide such as a silica and an alumina on a plastic film for improving the food long term storage property have been used. As an example, an alumina deposition film or a silica deposition film having a PET (polyethylene terephthalate resin) film used as the substrate film has been used.
However, it has been found that the gas barrier property is not sufficient when the gas barrier films conventionally used in the packaging field is used as a display substrate or for covering or sealing a display because the display itself is installed over a long term so that the exposure condition is severer than that of the food, such as influence of the potential or temperature rise at the time of use. Furthermore, the substance related to the display light emission and the light modulation is not chemically highly stable.
As another problem, to the synthetic resin film as the display substrate material or the synthetic resin film as the substrate for a gas barrier film for covering the display, in addition to the mechanical strength, the smoothness, the gas barrier property, or the like, the heat resistance or the moisture resistance are required in the stage of executing a process of laminating various layers on the synthetic resin film for providing a display, a process of providing a gas barrier layer, or the like. However, according to a common synthetic resin film, since the heat resistance or the moisture resistance is drastically poorer than the glass substrate, deformation or size change caused by heating in the metal thin layer forming process by deposition, or the like, heating in the heating step after coating a thermosetting resin coating material, or the like, or deformation or size change caused by moisture absorption due to contact with an aqueous solution in the metal thin layer etching process or the resist developing process cannot be avoided so that the problems such as deterioration of flatness of the obtained display or the gas barrier film, peel off due to creep with respect to the laminated metal thin layer and deviation with respect to a preset size can be generated.